html,
body {
    height: 100%;
}

body {
    display: flex;
    display: flex;
    -ms-flex-align: center;
    align-items: center;
    padding-top: 40px;
    padding-bottom: 40px;
    background-color: #f5f5f5;
}

div{ width: 300px;
    border: 25px solid green;
    padding: 25px;
    margin: 25px;}
